The present invention relates to a data processing system of the type having a plurality of host processors connected through first and second storage control units to a plurality of disk devices, the system being provided with a command queue store for storing host processor commands which have been sent to the storage control units for execution at the disk devices. Both storage control units have access to the command queue for the purpose of executing commands queued therein. More particularly, the present invention relates to a system as described above wherein plural connection paths may exist between some of the host processors and the storage control units and/or there may be no connection paths between at least one of the host processors and one of the storage control units. The present invention provides a host identification table which defines the connection paths between each storage control unit and the host processor and this table is accessed to determine an available connection path over which status may be reported to a host processor.
In a system wherein a processor issues commands directing the transfer of data between the processors and disk devices, and storage control units are interposed between the processors and the disk devices, it is common practice to report back to a processor the status of the storage control unit with respect to execution of a command issued by the processor. The routing of status from a storage control unit to a processor becomes more complex when processor commands are queued for later execution by either storage control unit and more than one connection path exists between the storage control unit and the processor or there are no connection paths between at least one of the storage control units and at least one of the processors. Where a storage control unit begins processing an interrupt from a disk device and there is no connection path between that storage control unit and a processor to which status must be reported, it is desirable for the first storage control unit to relinquish control so that the second storage control unit may report the status.